The objective of this project is to define the relationships between the structural properties of drugs and their ability to interact with membrane systems of the heart and to alter their biochemical properties. A wide variety of compounds within the defined grouping of propanolo/derivatives, bretylium derivatives and derivatives of known local anesthetic agents have been investigated for their ability to alter Ca ions uptake, Ca ions binding and Ca ions dependent ATPase of sarcoplasmic reticulum and sarcolemma preparations from dog heart. Many of the compounds were also studied in terms of their effects upon Na ion uptake by sarcolemma preparations. The relationships between Ca ions metabolism and the turnover of portions of the membrane phospholipids have been investigated. The Ca ions dependent base exchange reactions have been studied in some detail.